Abstract

Ce_1 − xZr_xO₂ solid solutions are produced continuously by hydrolysis of mixtures of cerium ammonium nitrate and zirconium acetate in near-critical water at ca. 300 °C and 25 MPa using a flow reactor. Rapid hydrothermal coprecipitation leads to nano-particulate Ce_1 − xZr_xO₂ (x = 0–1), the composition of which is largely determined by the initial relative concentrations of Ce⁴⁺ and Zr⁴⁺ ions in the starting solution. The freshly prepared materials are crystalline, possess very small particle sizes, and have high surface areas. The effects of calcining the products in air at high temperature have been studied. Apart from the 1∶1 Ce∶Zr solid solution, the phases of Ce_1 − xZr_xO₂ remain stable on calcining to 1000 °C, but the particles sinter and the surface areas decrease significantly. The materials have been characterised by Powder X-ray Diffraction (PXD), IR and Raman Spectroscopy, microanalysis, Thermogravimetric Analysis (TGA), X-ray Fluorescence (XRF) and BET (surface area measurements). In selected cases, high resolution Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) images were recorded to examine the particle morphology.